1. Field of the Invention
This invention relates generally to magnetic particles, and in particular to a method for fabricating magnetic particles for applications to affinity binding.
2. Description of Related Art
Magnetic particle (also known as magnetic bead) techniques have been established as valuable tools in several areas of biotechnology. The efficacy of these techniques derives from the basic property that the beads may be chemically attached or conjugated to various biochemical molecules with selective target recognition capabilities (such as proteins and nucleic acids) and added to extremely complex reaction mixtures (such as whole blood or fragmented cells in solution) so that the resulting affinity bound complexes become magnetic entities. In separations these complexes are selectively captured by a magnetic field followed by removal of unwanted impurities. Other applications, which include spatial confinement and magnetically induced aggregate formation, also exist.
The uses of magnetic bead technologies in nucleic acid scientific research include purifications for sequencing DNA, for isolating expressed RNA or proteins in differentiating cell lines, for constructing differential c-DNA libraries, for sorting chromosomes and large DNA molecules, and for isolating DNA binding proteins. There is currently a very large medical effort at whole cell separations for treatments such as bone marrow transplantation and organ transplant tolerance generation.
One limitation associated with the present technology is that magnetic separation based on only a single target is carried out at a given time, making potential multiple separations difficult, time consuming, and expensive. Further, a second separation on a given subject may not achieve optimal results, because the errors of the separations may be additive. If sufficiently distinctive magnetic particles could be produced and coupled to distinct xe2x80x9crecognitionxe2x80x9d molecules then it might be possible to separate the particles, and their bound targets, into different groups which reflect the type and number of bound magnetic particles. One example of the advantages offered by this capability is found in the literature pertaining to bone marrow transplantation. Here it found that separations based a single cell surface marker are routinely accomplished by magnetic bead techniques while separations based on multiple cell surface markers resort to fluorescence activated cell sorters which must analyze cells on an individual basis.
It can be seen, then, that there is a need for magnetic particles that have distinct and controllable magnetic properties and that can be attached to genetic material or other objects of interest.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for fabricating distinctive magnetic particles for affinity binding applications. The invention is discussed in detail for the application of biological separations, but is not limited to this application. The method comprises the steps of making a plurality of first magnetic beads having a first magnetic moment, making a plurality of second magnetic beads having a second magnetic moment, attaching a first acceptor molecule to the first magnetic beads, attaching a second acceptor molecule to the second magnetic beads, placing the first magnetic beads and the second magnetic beads into a solution, and applying an external magnetic field to the solution, whereby the first and second magnetic beads are caused to move at different rates by application of a magnetic field. The velocities of the beads depend upon viscous drag forces, the applied magnetic field and field gradient, and on the magnetic moments of the first and second magnetic beads, which may also depend on the magnetic field. Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples in accordance with the invention.